"Speak to the Levites and tell them: When you take from the Children of Israel the tithe that I have given to you from them as your inheritance, then you shall offer up from it a gift for G d, a tenth of the tenth"—B'Midbar/Numbers 18:26.
The Levites are commanded to separate a tenth from the tithe that they receive from the Israelites, and to give it to the priest. This tithe is called Maaser min Ha'Maaser or Terumat Maaser.(http://tinyurl.com/l6o2qjw)
The cohenim and levi'im survived on the work of the Israel'im (as they do today sitting in yeshivot in Israel). The difference between now and then was that then the cohenim and levi'im had specific jobs to perform in the Temple, albeit on rotation due to their numbers.
It is interesting to watch as people give a small donation during the morning ויברך דויד (And David blessed) recitation.
In my Moroccan sedurim we are told to give three (3) coins; two together and the third by itself. The sedurim give no clue as to the coin's value against, say, the Temple shekel - just "three coins."
Others put a dollar (or more) into the box. Considering most of the money - coins and bills - comes from regulars, the larger denominations suggest a visitor or perhaps a regular observing a special occasion.
But almost everyone in the minyan contributes something - even pre-bar mitzvah boys who have very limited incomes; I don't see them asking their fathers for money to contribute.
Obviously three coins a day probably - G-d willing it won't - do not make up a tenth (tithe) of the person's annual income (after taxes), other donations to various organizations that assist the needy are expected.
Locally (Hollywood FL) we have a Jewish food bank - We Are One. As with most Jewish assistance organizations - note I am NOT writing "charity" since Judaism doesn't consider helping one's fellow "charity" but an "obligation"; tzdekah means "justice" not "charity" - We Are One has more demands than resources.
The bottom line, which can be derived from the Torah commandment, is that even people receiving assistance must give a portion of their share to help support others (even if it means in truth giving money to themselves).
Aside from the opportunity to perform a postitive mitzvah - commandment - we can gain the satisfaction of knowing we are doing our part for the community - even if it only is three coins-a-morning.
We Are One
We Are One web site: http://weareonecharity.org/about-food-bank-hollywood-fl/
Sun-Sentinel article on We Are One may be read at http://tinyurl.com/qjyebbg
